Such a gas turbine forms part of the known gas turbine engine shown in FIG. 1, which Fig is a longitudinal cross section through the engine. Referring to FIG. 1, the engine comprises an air inlet 1, a compressor stage 3, combustors 5, a series of guide vanes 7, a series of rotor blades 9, a rotor shaft 11, and an exhaust 13. Air enters air inlet 1, is compressed in compressor stage 3, and mixed with fuel and combusted in combustors 5. Hot gases produced by the combustion are directed by guide vanes 7 so as to drive rotor blades 9 and hence rotor shaft 11. Rotor shaft 11 both (i) provides mechanical torque so as to deliver the work done by the engine, and (ii) drives compressor stage 3 so as to draw further air in through air inlet 1. Following rotor blades 9, the hot gases leave the engine via exhaust 13.
FIG. 2 illustrates in greater detail the part of the engine containing the guide vanes 7 and rotor blades 9. Hot gases pass in the direction of arrow A, being directed by guide vane 7 onto rotor blade 9. Rotor blade 9 includes a shroud part 15 and an aerofoil part 17. Guide vane 7 includes passageways there through by means of which a cooling fluid can be passed through the guide vane to cool it. Entrance to the passageways is via the radially inner and outer ends of the vane, as indicated by arrows 19, 21. Exit from the passageways is via slot 23.
It is desirable to cool the shroud part 15 of rotor blade 9 to increase the life of the blade. One attempt to do this comprised the supply of cooling fluid to the upstream end of the radially outer side of shroud part 15, as indicated by arrow 25. This was found to provide poor cooling as it tended to cool only the radially outer tips 27 of fins 29 of the shroud part. Another attempt to cool the shroud part comprised the supply of cooling fluid via holes in the so called platform 31 of the guide vanes, as indicated by arrow 33. This was also found to provide poor cooling as the cooling fluid tended to remain in region 35, swirling in this region and failing in large part to reach shroud part 15.